1. Field of the Invention
The present invention relates to an electromagnetic wave generating device. The present invention also relates to a device including an electromagnetic wave generating device and an electromagnetic wave detecting device integrated therein, and to an electromagnetic wave detector.
2. Description of the Related Art
In recent years, there has been developed an inspection technology for nondestructively analyzing and identifying a substance using an electromagnetic wave ranging from the millimeter wave band to the terahertz (THz) wave band (0.03 THz to 30 THz). A substance such as a biomolecule contains, due to its structure and state, an absorption spectrum in the terahertz wave band. The terahertz wave is safer than an X-ray, and hence it is expected to apply the terahertz wave to the imaging technology.
A technology of integrating a device for generating a terahertz wave and a device for detecting a terahertz wave on a transmission line is disclosed in Applied Physics Letters, vol. 70, p. 2233, 1997. FIG. 20 is a schematic view of the device disclosed in Applied Physics Letters, vol. 70, p. 2233, 1997, which is viewed from above.
The device illustrated in FIG. 20 includes a first electrode 2201, a second electrode 2202, a terahertz wave generating unit 2204, and a dielectric 2205. Voltage is applied to the first electrode 2201 and the second electrode 2202. An irradiation location 2203 is a location between the first electrode 2201 and the second electrode 2202 to which light is irradiated. By irradiating light to the irradiation location 2203, a terahertz wave is generated at the terahertz wave generating unit 2204.
The first electrode 2201 and the second electrode 2202 also serve as electrodes for propagating the terahertz wave. A terahertz wave generated at the terahertz wave generating unit 2204 is coupled to a transmission line including the electrodes, and thus the terahertz wave propagates through the transmission line.
In the case disclosed in Applied Physics Letters, vol. 70, p. 2233, 1997, the generated terahertz wave propagates mainly in two directions due to the structure of the device. That is, one terahertz wave is coupled to the first electrode 2201 to propagate in a first direction 2206, and another terahertz wave is coupled to the second electrode 2202 to propagate in a second direction 2207. In some cases, a terahertz wave required in an application of the device is only a component which propagates in the first direction 2206. In those cases, a terahertz wave which propagates in the second direction 2207 with respect to the generated terahertz wave is an energy loss, which is undesirable. When the terahertz wave is propagated in the first direction 2206 as much as possible, the energy of the generated terahertz wave can be used more effectively, which is efficient.